The roof is one of your most important architectural elements of your project as it serves as protection against natural elements. Because of this it is important to take into consideration the roof type, pitch, aesthetics and type of material when planning your project. Sheet metal roofing has gained popularity amongst architects as it is economic, durable and versatile and enhances the aesthetics of a project. Sheet metal roofing can be used for any type of residential, industrial or commercial building and depending on the material the roof slopes can be as little as 1°, however National Building regulations advises a 5° pitch. Depending on the climatic conditions, supporting structures and design influencing roof design, the installation and the type of fastening system used for your metal roof is a deciding factor to consider in the early design & planning phases or your metal roof
There are two main types of installation techniques/fastening systems to consider on your project, which is either a Pierced fixed roofing technique (Positive fix) or a Concealed fixed (Non-positive fix) roofing technique.
Pierced fixed type roofs are typically used in conventional roof types and is mainly used for roofing profiles such as Inverted Box Rib (IBR), Corrugated and Widespan roofing profiles. A Fastener (nails/screws) is used to fix/positive fix the sheet metal to the purlin/lipped channel/timber truss by penetrating through the metal sheeting. Perforations are then unavoidable in the crest of the sheeting. With pierced fixed roofing, the roof is fixed directly onto the purlin/truss which then limits thermal expansion on the roof and due to this it may cause that the fastening points wear out and can create leakage over time.
Example of IBR roof sheeting profile:
Concealed fixed type roofs are generally used for commercial and industrial projects such as warehouses, factories, schools and shopping centers. For Concealed fixing/non-positive fixing methods there is no perforation of the sheeting and no fasteners penetrate through the sheeting (such as Craft-Lock®/Reehfalz concealed fixing systems). For a concealed fix system such as Craft-Lock®, the profile is formed with a female & male lip on the longitudinal edges of the sheet, the male lip is fastened by means of a cleat onto the purlin and the female rib is then seated over the male rib in a sideways interlocking manner. The female rib conceals the fixing cleat and this system then allows freedom of movement for thermal expansion and contraction and eliminates stress on the fastening systems.
Example of Craft-Lock® concealed roofing system:
The lifespan of your roof is dependent on the type of fastener used for your roof. What seems as such a small cost element of your roof can in the long run cost you much more when the wrong type of fastener is used. In consideration when choosing a fastener, it is important to note the type of fastener and compatibility of the type of metal material and coatings used with the fastener. It is often overlooked that fasteners need to resist climate, material compatibility and loading conditions. A roof can be done with the best roofing system and material, but if the fasteners fail early, it defeats the purpose.
Refer to more information on the SAISC article at https://www.saisc.co.za/secondary-fastners/
Depending on the project requirement, each roof type needs to be fit for purpose. If you need a more flexible roof design with natural curves and that withstand heavy wind loads- metal roofing is then the product of choice. Metal roofing is versatile, lightweight and more economic than any other roofing material and is up to 80% lighter than using heavier roofing types for example concrete tiles. Because of the light-weight feature of steel, it in turn saves on the roof structure, construction time and the cost of the project. As steel is readily formable, metal roofing offers the designer a variety of colours, material finishes (gloss, matt & textured), the freedom of design and creativity which makes it suitable for a wide variety of roof design features.
There are 5 factors to consider when specifying metal roofs for your project:
Herewith below a typical Craft-Lock® Concealed fix roof sheeting specification for a project:
Craft-Lock® Concealed fix roof sheeting with a male/female sideways interlocking mechanism, forming a double capillary action break manufactured from
(1)0.58mm thick (2)ISQ 300 steel with (3)Chromadek® finish, colour (Fish Eagle White)
with a (4) Z 275 (5) Galvanized coating.
(1) Refers to your thickness of choice
(2) Refers to the correct material grade
(3) Refers to the desired finish
(4) Refers to the desired protective coating mass
(5) Refers to the desired protective coating
Profile type, material thickness, coating types, yield strengths and paint finishes can often be a confusing combination to get right when it comes to specifying the type of roof to be used on a project. It is therefore critically important to specify each aspect correctly. Ambiguity in specification leads to either honest mistakes or willful manipulation by contractors or subcontractors on projects, where lower quality products end up on projects than were intended by architects or developers. By taking the time to write a clear specification and omitting wording such as “similar or approved” will lead to clients and professionals having roofs on their projects that they chose initially.